The active medium in a CO.sub.2 laser is a gas mixture of carbon dioxide, nitrogen, helium and, in some instances, other gases such as carbon monoxide or xenon. When an electrical discharge is formed in the gas to excite the active medium, some of the components in the mixture dissociate. In particular, CO.sub.2 dissociates into CO and oxygen. The dissociation of the gas results in the depletion of the volume of active medium and is one of the primary reasons for failures in sealed CO.sub.2 lasers.
Attempts at reducing the deleterious effects of gas dissociation have used techniques such as the use of large volumes of gas reserves, and catalysis of the dissociated components. The technique most often used in CO.sub.2 lasers, is the use of catalysts to speed up the recombination of the dissociated components. Carbon monoxide and oxygen do not recombine at room temperature; under certain conditions, however, they will combine in the presence of certain catalysts. Platinum is the best known catalyst; however, it requires operation of the laser at elevated temperatures not feasible in a sealed CO.sub.2 laser. Hopcalite, a commercially available mixture of magnesium oxide (MnO.sub.2) and cuprous oxide (CuO), is sometimes used as a catalyst. The main problem is that the catalyst powder is found to disperse itself throughout the laser envelope and thus it degrades the performance of the laser, especially when a portion of the catalyst powder is deposited on the optics.
An article entitled "Sealed Multiatmosphere CO.sub.2 TEA laser: Seed-Gas compatible system using unheated oxide catalyst" by R. B. Gibson et al., Appl. Phys. Letters 32(11), 1 June 1978, describes a laser system which confines the catalyst powder outside the main laser envelope and requires pumping to circulate the gas past the catalyst powder.